Two stage energy storage device

ABSTRACT

An electronic device, which captures and accumulates varying levels of electrical energy in suitable short-term storage means until the energy is of such a level that it can be efficiently transferred to at least one long-term storage device means, such as electro-chemical batteries. The invention further permits simultaneous transfer to a variety of electro-chemical batteries, which can possess different storage chemistries.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the priority of provisional U.S. applicationSer. No. 60/479,541, filed on Jun. 17, 2003 and entitled “A Two StageEnergy Storage Device” by Andrew C. Kular, the entire contents andsubstance of which are hereby incorporated in total by reference.

FIELD OF THE INVENTION

This invention relates to electronic power management and storagedevices.

BACKGROUND OF THE INVENTION

Portable electronic and electrical devices (PEDs) require lightweightand compact power sources. While some very low power devices (e.g.calculators) can be powered directly from energy sources such asphotovoltaic cells (PV), for many practical PEDs a higher capacityenergy storage device such as an electro-chemical battery (battery) isrequired. Many PEDs employ rechargeable batteries as a means for storingenergy during a recharging process and then release the stored energywhile the PED is in use.

As is well known to those skilled in the art, electro-chemical batterieshave specific requirements for safe and efficient charging. Thesespecific requirements vary by the specific battery technology but in allcases, safe and efficient charging requires applying energy withinspecific voltage and current levels for specific periods of time. Forthis reason, the typical energy source employed for charging batteriesis generally from stationary and much larger source of energy such as,for example, electric utility mains power or an automobile battery.

The need to have access to a large power source at a fixed stationarylocation is often not convenient since the very nature of a PED is thatthe PED is portable and often in use some distance away from a largestationary source of power to recharge the battery. As is also wellknown to those skilled in the art, there are many potential sources ofenergy that might be employed to recharge a battery. However, many ofthese alternatives to large fixed sources of energy are often of anintermittent nature and may be of too low a level of power to betransformed by conventional methods to suit the specific voltage andcurrent levels needed to safely and efficiently charge a battery.Examples of such potential alternative sources of energy arephotovoltaic cells, manually operated electromagnetic mechanicalgenerators, and even brief connections to electric power utility mains(whenever a user can briefly pause near such mains).

Various simple means to recharge an electro-chemical battery usingintermittent and variable sources such as photovoltaic cells arewell-known in the prior art. An example of such a system is found inU.S. Pat. No. 3,921,041 entitled “Charging Circuit for Battery-OperatedDevices Powered by Solar Cells”, issued to Geoffrey Mellors, et al. onNov. 18, 1975. FIG. 1 depicts a circuit employed by Mellors in thispatent.

In the system of FIG. 1, the battery 102 can only be effectively chargedwhen there is sufficient light intensity such that the voltage outputfrom the PV cell 106 exceeds the battery voltage plus the forward biaseddiode threshold of device 104. In this case, any energy generated by thePV that is below voltage and current threshold is wasted since it cannotcharge the battery B1.

A further problem with the approach of FIG. 1 is that some modernbattery technologies such as Li-Ion cannot be safety charged withoutcharge management electronics to limit voltage and current levels intothe battery B1. Such charge management electronics may have even moredemanding voltage and current levels than charging the battery directly.For this reason it is not uncommon to employ charge managementelectronics between the PV cell and the battery. An example of such asystem is illustrated in FIG. 2. In this figure a high efficiencyelectronic circuit, typically in the form of a DC to DC converter 204and associated regulation and sensing circuitry (not shown), is used toconvert the DC voltage from the array of PV cells 202 to a voltage moresuitable than a direct connection between the PV cells and the batteryas in FIG. 1.

While the approach in FIG. 2 is an improvement over that of FIG. 1, itstill suffers from the inability to effectively make use of low levelsor brief periods of illumination for two related reasons: 1) If thelevel of illumination is of a low level the voltage generated by the PVcell will not be sufficient to operate the DC to DC converter as anypractical electronic device requires voltages well above zero to operatewith an efficiency. And 2) If there are very high levels of illuminationfor a brief period, the PV cells might produce more energy than thebatteries can safety absorb during the brief period of illumination. Inthis case the excess energy generated by the PV cells will be wastedsince it cannot be captured and stored in the battery.

U.S. Pat. No. 3,921,049 entitled “Battery-Less Solar Power System” andissued to Miguel Timm on Apr. 9, 2002 recognizes the value of capturingvariable and intermittent energy such as from a PV cell source andaccumulates this energy in a capacitor. However, this invention employsthe stored energy to operate a device directly. When this stored energystorage is sufficiently depleted, the device ceases operation.Consequently, its use is limited to specific applications where suchinterruptions are allowable.

There is a need in the prior art to provide the means for the efficientcapture, accumulation and use of potential alternative sources of energywhose supply may be intermittent and variable in magnitude. Suchalternative sources of energy include photovoltaic cells, manuallyoperated electro-magnetic mechanical generators, wind power, and wavepower. Further, there is a need to provide an effective means to usethis captured energy to properly and efficiently recharge the batterypower source(s) of an electrical device.

SUMMARY OF THE INVENTION

The present invention provides a system and method by which intermediateand variable sources of energy can be accumulated and used as aneffective source of power for various electrical devices which arebattery powered. According to the present invention, the variable andintermittent energy source is supplied to an intermediate or first stageof energy storage. This first stage of energy storage is then connectedvia a battery charge management component to a second stage storagedevice in the form of an electro-chemical battery.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, incorporated in and forming part of thespecification, illustrate several aspects of the present invention and,together with their descriptions, serve to explain the principles of theinvention. In the drawings:

FIG. 1 illustrates a prior art system employing PV technology torecharge a battery;

FIG. 2 illustrates a prior art PV charging system which uses chargemanagement electronics;

FIG. 3 is an overall block diagram of the present invention; and,

FIG. 4 is a flow diagram illustrating an example of the operation ofcontrol logic component of the embodiment of FIG. 3

DETAILED DESCRIPTION

One embodiment of the invention is depicted in FIG. 3. In this figure,functional features are illustrated at the top of the figure whilecircuit components corresponding to those features are illustratedbelow. As illustrated, this embodiment comprises a PV array 302 as anexample of a variable and intermittent energy source. Alternativeembodiments of the invention permit the use of PV material in itsprimary state (i.e., without an array structure). The energy collectedfrom this source is supplied to a first stage soft energy storage means304, such as a high value capacitor 310—as might be realized by anelectrical double layer capacitor (also known as an Ultra capacitor or asupercapacitor). The invention is not limited to such a double layercapacitor as additional embodiments of the invention utilize variouselectrical devices which exhibit capacitance or pseudo-capacitancebehavior and which have a low Electric Series Resistance (ESR).

The first stage energy storage means is referred to herein as softstorage to distinguish it from the hard storage properties of a typicalbattery. The important properties of said first stage energy storagemeans are that it can accept and efficiently accumulate even low levelsof energy from the energy source 302 without a threshold and withoutwaste. The first stage energy storage means 304 is connected aswitchable DC to DC converter 306 and 312. Suitable power regulation,transformation, and conditioning elements in the DC to DC converteraccept the energy from the first stage of storage device and employ itto efficiently and safely charge a second stage storage device.

In addition to the DC to DC converter 312 illustrated in the circuitdiagram of FIG. 3, a control logic component 314 is also depicted. Thecontrol logic component 314 monitors the voltage level on the firststage energy storage means 310 and when a voltage sensor 316 recognizesthat the voltage exceeds a preset threshold; it activates a FET switch313 and the DC to DC converter 312. In a further embodiment of theinvention, the control logic also provides a means to protect the firststage energy storage means 310 from over-voltage conditions that mightdamage it. In particular, a switch 318 is employed to bleed excessenergy and thereby limit the maximum voltage across the first stageenergy storage means 310.

An additional feature of the control logic is a current flow sensor 320.The current flow sensor can determine if the energy source 302 is strongenough to source current into the energy storage means 310. Should theenergy from the source cause the current flow to reverse therebydischarging the energy storage means 310, the current flow sensor 320signals the control logic component 314 to transfer the energy from thestorage means 310 even if the voltage is below the optimum threshold.

Also illustrated in FIG. 3 is a second stage energy storage device, ahard storage device 308 shown with a Li-Ion battery as an example. Asused herein, a hard storage device is defined as the energy storagedevice employed for long term storage with a capacity of significantlymore energy (higher density) than the first stage soft storage means304.

It should be noted that while FIG. 3, depicts a single Li-Ion battery asthe second storage device being charged by the invention, other types ofbatteries having various battery chemistries are contemplated by theinvention. The control logic component 314 properly controls the voltageand current in the charging process of the particular second storagedevice. Further, the invention is not limited to only a single secondstorage device as multiple storage devices, each potentially havingdifferent charging requirements, are contemplated by the invention.Accordingly, the control logic component properly controls the voltageand current related to the charging requirements of each of these secondstorage devices.

The control logic component 314 will now be discussed in greater detail.In operation, and again referring to the embodiment depicted in FIG. 3,a current from the PV array 302 is detected by a current sensingresistor 315 and the resultant voltage signal is amplified in a linearfashion by the operational amplifier 320. The amplified signal producedis fed to an analog to digital converter within the control logiccomponent 314. The control logic component permits setting of variousthreshold values, to include the operating parameters of the varioussoft or hard energy storage components contained in the system. Thisfeature of the invention is implemented via programmable software code,a programmable logic chip (i.e. firmware), hardware pin connectors, andcombinations thereof. Hard storage materials tend to be chemical basedin nature and exhibit greater electrical energy storage density. Softstorage materials store electrons on the basis of available surface areaand therefore exhibit low electrical energy storage density.

Based on the signal analysis, the control logic component 314 candetermine both the magnitude and direction of electrical energy flowswithin the system. As a result it can effect the various functions notedabove (e.g., detecting excess voltage or reverse current flow withrespect to storage means 310). Further, the control logic component 310can then apply this energy to operate any application requiringelectrical energy which may be desired, for example, portable electronicdevices (cellular telephones, hand-held computing devices, etc.).

As noted above, an important feature of the present invention is itsability to recharge one or more batteries, of differing batterychemistries. FIG. 4 illustrates this feature with respect to two batterytypes: a Rechargeable Alkaline Manganese (RAM) battery and a NickelMetal Hydrate (NMh) battery. At the Start location (item 400) variousinitialization steps are performed to include setting the Charging Flagto an Off State. The charging flag is the indication to the system tocommence/continue the charging operation of the batteries. The depictedalgorithm is cyclically performed under the control of a timer. Eachsuch cycle commences at point 401.

At the commencement of each cycle, a determination is made step (401)whether or not there is available charging current. Referring to FIG. 3,this would correspond to voltage sensor 316 recognizing that the firstenergy storage means has accumulated sufficient voltage. In the eventsuch available voltage is lacking, the charging flag is set OFF (Step422) and the system simply waits until the next cycle.

With available charging voltage present, the system then commences (step404) to the appropriate charging decision branch for each availablebattery that has been assigned to be charged by the system. In thisexample two such batteries are present. Looking first at the RAM batteryexample, the system determines (at step 406) if the battery is at itsmaximum voltage (i.e., Vmax_ram). If it is, the charging flag is set toOFF. If it is not, charging may not commence as the system then looks(at step 414) to see if the battery voltage has been reduced to athreshold voltage value (i.e., V_enable_ram). By way of example, thisthreshold may be set to 90% of the maximum value and precludesunnecessarily charging a battery that does not require it. If thebattery has not yet dropped to that level, the algorithm merely awaitsthe commencement of another cycle. If the battery does fall below thethreshold, the charging flag is set to ON. Charging would then continuethrough successive cycles until the battery has attained its maximumvoltage (step 406) or charging voltage is not longer available (step402).

As depicted in FIG. 4, if a NMh battery is detected at step 404, itscharging operation is conducted in the same manner, but with differentthreshold parameters being compared against (e.g, at steps 408 and 416).It should be noted that the algorithm illustrated in FIG. 4 permitssimultaneous charging of both batteries.

The foregoing descriptions of the present invention have been presentedfor purposes of illustration and description. They are not intended tobe exhaustive or to limit the invention to the precise forms disclosed.Many alternatives, modifications, and variations will be apparent tothose skilled in the art in light of the above teaching. Accordingly,this invention is intended to embrace all alternatives, modifications,and variations that fall within the spirit and broad scope of theattached claims.

1. An electronic device which captures and accumulates variable levelsof electrical energy in a soft storage means until the accumulatedenergy is of such a level that it can be efficiently transferred to ahard storage means, said device comprising: a) a source of variable andintermittent energy; b) a first stage energy storage means suitable forcapturing and accumulating the energy from the source; c) a second stageenergy storage means, which is capable of receiving a charge and storingthis charge for later use; and, d) an electronic means which senses andmonitors the energy accumulated in the first stage storage means andthen activating a charge management electronics means when there issufficient energy in the first stage storage to efficiently charge thesecond stage energy storage means.
 2. The device of claim 1 wherein saidfirst stage energy storage means comprises an electrical device whichexhibits capacitance or pseudo-capacitance behavior and has a lowEquivalent Series Resistance (ESR).
 3. The device of claim 1 furthercomprising a control circuit that senses an over-voltage condition inthe first stage energy storage means and limits the voltage to a safelevel.
 4. The device of claim 1 further comprising a control circuitthat senses the direction of current “into” versus “out of” the firstenergy stage storage means and activates the transfer of any usefulenergy from the first stage storage means to the second stage storagemeans even if the voltage in the first stage storage means is notoptimal for such a transfer.
 5. The device of claim 1 wherein saidenergy source is selected from the group consisting of photovoltaiccells, manually operated electromagnetic mechanical generators, windpower, wave power, electric power utility mains, AC transformers, DCtransformers, and combinations thereof.
 6. The device of claim 1 furthercomprising at least two first stage energy storage means.
 7. The deviceof claim 1 further comprising at least two second stage energy storagemeans.
 8. The device of claim 7 wherein said charge managementelectronics comprises a programmable means for setting parameters usedto effect said efficient charging of the second stage storage means. 9.The device of claim 8 wherein said programmable means is selected fromthe group consisting of programmable software code, programmable logicchips, hardware pin connectors, and combinations thereof.
 10. The deviceof claim 8 wherein said charge management electronic means permitsindependent charging of at least some of said at least two second stagestorage means.
 11. A method for capturing and accumulating variablelevels of electrical energy in a first stage energy storage means untilthe accumulated energy is of such a level that it can be transferred toa second stage energy storage means, said method comprising: a)capturing and accumulating the energy into the first stage energystorage means; b) sensing and monitoring the energy accumulated in thefirst stage storage means; and, c) activating a charge managementelectronics means when there is sufficient energy in the first stagestorage to efficiently charge the second stage energy storage means. 12.The method of claim 11 wherein said first stage energy storage meanscomprises an electrical device which exhibits capacitance orpseudo-capacitance behavior and has a low Equivalent Series Resistance(ESR).
 13. The method of claim 11 further comprising: sensing anover-voltage condition in the first stage energy storage means; and,limiting the voltage to a safe level.
 14. The method of claim 11 furthercomprising: sensing the direction of current “into” versus “out of” thefirst energy stage storage means; and, activating the transfer of anyuseful energy from the first stage storage means to the second stagestorage means even if the voltage in the first stage storage means isnot optimal for such a transfer.
 15. The method of claim 11 wherein saidenergy source is selected from the group consisting of photovoltaiccells, manually operated electromagnetic mechanical generators, windpower, wave power, electric power utility mains, AC transformers, DCtransformers, and combinations thereof.
 16. The method of claim 11further comprising at least two first stage energy storage means. 17.The method of claim 11 further comprising at least two second stageenergy storage means.
 18. The method of claim 17 further comprisingutilizing a programmable means for setting parameters used to effectsaid efficient charging of the second stage storage means.
 19. Themethod of claim 18 wherein said programmable means is selected from thegroup consisting of programmable software code, programmable logicchips, hardware pin connectors, and combinations thereof.
 20. The methodof claim 18 wherein said charge management electronic means permitsindependent charging of at least some of said at least two second stagestorage means.